One of the two atrio-ventricular valves in the heart is the mitral valve, which is located on the left side of the heart and which forms or defines a valve annulus and valve leaflets. The mitral valve is located between the left atrium and the left ventricle, and serves to direct oxygenated blood from the lungs through the left side of the heart and into the aorta for distribution to the body. As with other valves of the heart, the mitral valve is a passive structure in that it does not itself expend any energy and does not perform any active contractile function.
The mitral valve includes two moveable leaflets that open and close in response to differential pressures on either side of the valve. Ideally, the leaflets move apart from each other when the valve is in an open position, and meet or “coapt” when the valve is in a closed position. However, problems can develop with these valves, which can generally be classified as either stenosis, in which a valve does not open properly, or insufficiency (also called regurgitation), in which a valve does not close properly. Stenosis and insufficiency may occur independently or concomitantly in the same valve. The effects of valvular dysfunction vary, with mitral regurgitation or backflow typically having relatively severe physiological consequences to the patient. Regurgitation, along with other abnormalities of the mitral valve, can increase the workload placed on the heart. The severity of this increased stress on the heart and the patient, along with the ability of the heart to adapt to the increased stress, determine the treatment options that are available for a particular patient. In some cases, medication can be sufficient to treat the patient, which is the preferred option when it is viable; however, in many cases, defective valves have to be repaired or completely replaced in order for the heart to function normally.
One situation in which repair of a mitral valve can be viable is when the defects present in the valve are associated with dilation of the valve annulus, which not only prevents competence of the valve but also results in distortion of the normal shape of the valve orifice. Remodeling of the annulus is central to these types of reconstructive procedures to the mitral valve. When a mitral valve is repaired in this way, one common result is a reduction in the size of the posterior segment of the mitral valve annulus. As a part of the mitral valve repair, the involved segment of the annulus is diminished (i.e., constricted) so that the leaflets may coapt correctly on closing, and/or the annulus is stabilized to prevent post-operative dilatation from occurring. Either result is frequently achieved by the implantation of a prosthetic ring or band in the supra annular position. The purpose of the ring or band is to restrict, remodel and/or support the annulus to correct and/or prevent valvular insufficiency. Such repairs of the valve, when technically possible, can produce relatively good long-term results.
However, repair of the mitral valve area is sometimes either impossible or undesirable or has failed, such as in cases where dilation of the valve annulus is not the problem, leaving valve replacement as the preferred option for improving operation of the heart. In cases where the mitral valve is replaced, it can generally be replaced with either mechanical valves or bioprosthetic or tissue valves. The surgical procedure for implantation of many of these mechanical and tissue valves involves opening the patient's chest to access the mitral valve through the left atrium, and sewing the new valve in position. In order to simplify surgical procedures and reduce patient trauma, methods and devices have recently been developed for replacing the mitral valve using minimally invasive and/or percutaneous replacement techniques and devices. In one exemplary valve replacement procedure, a replacement valve can be delivered in a compressed condition to the native valve site, where it is expanded for implantation into the target site in a patient. With specific regard the replacement of the mitral valve, a replacement mitral valve can be inserted into a balloon catheter and delivered percutaneously via the vascular system to the annulus of the native mitral valve, where the replacement valve can be expanded by a balloon.
Due to the relatively complicated path through which a delivery system must travel to reach the area of the mitral valve for either its repair or replacement, many delivery systems that are currently available cannot provide for consistent navigation to the desired area. Thus, there is a continued desire to provide for improved mitral valve delivery systems and repair or replacement procedures that accommodate the physical structure of the heart without causing undue stress to the patient during the operation on the heart.